The present invention relates to an improvement on a bonnet for an automobile.
An example of a conventional bonnet for an automobile is disclosed in a Japanese Patent Unexamined Publication No. Hei. 5-155355 reciting "an engine hood construction for an automobile". As shown in FIGS. 10 and 11, an engine hood 70 is constructed such that an engine hood inner panel 71 serving as a reinforcement member is placed so as to integrally underlie an engine hood outer panel 72. The engine hood inner panel 71 is constituted by a reinforcement portion 73 (frame) having a U-shaped cross section and formed in a grid-like fashion. A through hole 74 is formed in the bottom of an apex portion 75 where frame constituent members intersect each other and a through hole 76 is also formed in side wall portions of respective reinforcing portions 77, 78 in the vicinity of the apex portion 75 in order to attain a reduction in rigidity of the apex portion 75 to thereby alleviate impact against an obstacle.
However, even if the rigidity at the apex portion 75 is tried to be reduced by forming a through hole 74 in the bottom of the apex portion 75 of the frame constituent members and a through hole 76 in the side wall portions of the respective reinforcing portions 77, 78 in the vicinity of the apex portion, the side wall portions arranged in a grid-like fashion still remain too strong, and therefore, if an obstacle comes into collision with the engine hood in the vicinity of such side wall portions of the respective reinforcing portions 77, 78, impact produced by the collision cannot sufficiently be alleviated.
In addition, if the through holes 74, 76 formed, respectively, in the bottom of the apex portions and the side wall portions are enlarged, this will make it impossible to maintain a rigidity originally required for the engine hood inner panel 71, resulting in an excessive reduction in rigidity of the engine hood.